1. Field of the Invention
The field of art to which this invention pertains is hydrocarbon processing. It particularly relates to lower capital cost in a process for the acid-catalyzed alkylation of isoparaffins with olefins.
2. Prior Art
The acid-catalyzed alkylation of hydrocarbonaceous materials is one of modern petroleum refining's most valued tools. The production of higher molecular weight isoparaffins, having valuable antiknock properties and used as motor fuel, is of considerable importance. A convenient source of such higher molecular weight isoparaffins is the acid-catalyzed alkylation of lower boiling isoparaffins, such as isobutane, with olefins such as propene and butenes. It is well known in the art that catalytic alkylation, using hydrofluoric or sulfuric acid as the catalyst, has become an important tool for preparing alkylated hydrocarbons.
Hydrofluoric and sulfuric acids are hazardous chemicals with properties peculiar to themselves which call for special handling and treatment. With improper treatment they can be lethal. For this reason processes for the use of such acids must be equipped with systems which effectively prevent the escape of these acids into the atmosphere. Common practice in the art is to provide an acid relief system which collects the effluent of all relief valves within the process from which acid may be expected to be released. As is well known in the art, relief valves are commonly fitted to processing zones which may operate at superatmospheric pressures. These valves open and allow an exhaust of material from the process at pressure levels above normal but below that at which structural damage to the processing zones would occur. It is quite common during the cessation or initiation of operation of a process that processing zones are periodically over pressured. During these periods of overpressure, the associated relief valves open and maintain safe pressure levels by exhausting material from the affected zones. The exhausts from acid-bearing relief valves pass to an acid relief system which carries the exhaust to a neturalizing zone, wherein the acid contained within the exhaust is neutralized and made safe for entry into the normal waste disposal facilities of the process. The metallurgy of acid relief systems must be such as to resist the effects of corrosion from the acid passing through it. Relatively exotic and very expensive metallurgical formulations are often used as materials in the construction of acid relief systems.
Zones within the process which do not commonly contain acid are likewise protected by relief valves, but these valves commonly exhaust into a so-called non-acid relief system. The non-acid relief and the acid relief systems of a hydrogen fluoride alkylation process are major pieces of equipment, and they represent significant portions of the capital investment involved in the realization of such a process. I have found that by a novel inclusion of thermal insulation in the design of the processing plant the size, and hence the cost, of the acid relief and non-acid relief systems can be reduced. The present invention provides for this reduction in cost, and it is fully as useful in the modification of existing processes for higher capacity as it is in the design of new installations.